Search results for "spin [structure function]"
showing 10 items of 1132 documents
[Fe III (bztpen)(OCH 3 )](PF 6 ) 2 : Stable Methoxide–Iron(III) Complex Exhibiting Spin Crossover Behavior in the Solid State
2010
Complex [Fe III (bztpen)(OCH 3 )](PF 6 ) 2 (1) crystallizes as the major yellow-brown product from spontaneous oxidation of its corresponding iron(II) counterpart in methanol solution. Magnetic measurements and EPR spectra demonstrate that 1 undergoes a poorly cooperative 6 A 1 ↔ 2 T 2 spin conversion in the temperature range 300-50 K, with characteristic thermodynamic parameters ΔH = 6.15 kJ mol -1 , ΔS = 39.88 J K -1 mol -1 , and T 1/2 = 154 K. The crystal structure of 1 has been investigated at 100 and 293 K.
[Fe(TPT)(2/3){M(I)(CN)2}2]⋅nSolv (M(I) = Ag, Au): new bimetallic porous coordination polymers with spin-crossover properties.
2013
Two new heterobimetallic porous coordination polymers with the formula [Fe(TPT)2/3{MI(CN)2}2]¿nSolv (TPT=[(2,4,6-tris(4-pyridyl)-1,3,5-triazine]; MI=Ag (nSolv=0, 1¿MeOH, 2¿CH2Cl2), Au (nSolv=0, 2¿CH2Cl2)) have been synthesized and their crystal structures were determined at 120¿K and 293¿K by single-crystal X-ray analysis. These structures crystallized in the trigonal R-3m space group. The FeII ion resides at an inversion centre that defines a [FeN6] coordination core. Four dicyanometallate groups coordinate at the equatorial positions, whilst the axial positions are occupied by the TPT ligand. Each TPT ligand is centred in a ternary axis and bridges three crystallographically equivalent Fe…
Nanoporosity, Inclusion Chemistry, and Spin Crossover in Orthogonally Interlocked Two-Dimensional Metal-Organic Frameworks
2015
[Fe(tvp)(2)(NCS)(2)] (1) (tvp=trans-(4,4-vinylenedipyridine)) consists of two independent perpendicular stacks of mutually interpenetrated two-dimensional grids. This uncommon supramolecular conformation defines square-sectional nanochannels (diagonal approximate to 2.2nm) in which inclusion molecules are located. The guest-loaded framework 1@guest displays complete thermal spin-crossover (SCO) behavior with the characteristic temperature T-1/2 dependent on the guest molecule, whereas the guest-free species 1 is paramagnetic whatever the temperature. For the benzene-guest derivatives, the characteristic SCO temperature T-1/2 decreases as the Hammet sigma(p) parameter increases. In general, …
Two- and one-step cooperative spin transitions in Hofmann-like clathrates with enhanced loading capacity
2014
Structural, magnetic, calorimetric and Mo¨ssbauer studies of the cooperative spin crossover naphthalene and nitrobenzene clathrates of the novel FeII Hofmann-like porous metal–organic framework {Fe(bpb)[Pt(CN)4]}2Guest are described (bpb = bis(4-pyridyl)butadiyne).
Structural and magnetic characterization of the tridimensional network [Fe(HCO2)3]n·nHCO2H
2013
In this work we report the structural and magnetic characterization of a new three-dimensional porous metal–organic framework (MOF) based on iron(III) and the formate anion, [Fe(HCO2)3]n·nHCO2H (1), which was obtained by solvothermal synthesis. The tridimensional structure crystallizes in the trigonal space group Rc and is formed by highly regular octahedral Fe(OHCO)6 units. These units contain six equal Fe–O distances, with angles slightly different from 90° or 180°. The packing of 1 corresponds to a 3D covalent network defined by face sharing between the parallelepipeds, which are formed by the interactions of Fe(OHCO)6 units through formate ligands, thus generating a 41263 topology. This…
Cooperative effects on the HS→LS relaxation in the [Fe(ptz)6](BF4)2 spin-crossover system
1992
Abstract The high-spin to low-spin (HS→LS) relaxation in the [Fe(ptz) 6 ](BF 4 ) 2 spin-crossover system deviates strongly from first-order kinetics because of cooperative effects of elastic origin. The shift in horizontal and vertical displacement of the potential wells of the initial and final state relative to each other due to the build-up of an “internal” pressure is estimated from spectroscopic measurements. The HS→LS relaxation as such is described by the theory of nonadiabatic multiphonon relaxation in the strong-coupling limit, with a Huang—Rhys factor S ≈ 45 which is much larger than the reduced energy gap p . The sigmoidal relaxation curves in [Fe(ptz) 6 ](BF 4 ) 2 result when a …
"Through-space" 31P spin-spin couplings in ferrocenyl tetraphosphine coordination complexes: improvement in the determination of the distance depende…
2008
Abstract From the analysis of several nickel and palladium halide complexes of a constrained ferrocenyl tetraphosphine, the existence in solution phase of unique 31P–31P “through-space” nuclear spin–spin coupling constants (JPP) had been previously evidenced. Due to the blocked conformation of the species in solution, and based on the NMR spectra obtained for the complexes and their corresponding solid state X-ray structures, these JPP constants had been shown to clearly depend on the mutual spatial position of the corresponding phosphorus atoms. Herein, the quantitative correlation disclosed at that time (P⋯P distance dependence of coupling constants) is remarkably confirmed, and mathemati…
An Octanuclear Metallosupramolecular Cage Designed To Exhibit Spin-Crossover Behavior.
2018
By employing the subcomponent self-assembly approach utilizing 5,10,15,20-tetrakis(4-aminophenyl)porphyrin or its zinc(II) complex, 1H-4-imidazolecarbaldehyde, and either zinc(II) or iron(II) salts, we were able to prepare O-symmetric cages having a confined volume of ca. 1300 Å3 . The use of iron(II) salts yielded coordination cages in the high-spin state at room temperature, manifesting spin-crossover in solution at low temperatures, whereas corresponding zinc(II) salts led to the corresponding diamagnetic analogues. The new cages were characterized by synchrotron X-ray crystallography, high-resolution mass spectrometry, and NMR, Mössbauer, IR, and UV/Vis spectroscopy. The cage structures…
Guest Removal and External Pressure Variation Induce Spin Crossover in Halogen-Functionalized 2-D Hofmann Frameworks.
2020
The effect of halogen functionalization on the spin crossover (SCO) properties of a family of 2-D Hofmann framework materials, [FeIIPd(CN)4(thioX)2]·2H2O (X = Cl and Br; thioCl = (E)-1-(5-chlorothiophen-2-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine) and thioBr = (E)-1-(5-bromothiophen-2-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine)), is reported. Inclusion of both the chloro- and bromo-functionalized ligands into the Hofmann-type frameworks (1Cl·2H2O and 2Br·2H2O) results in a blocking of spin-state transitions due to internal chemical pressure effects derived by the collective steric bulk of the halogen atoms and guest molecules. Cooperative one-step SCO transitions are revealed by either guest r…
Exploiting Pressure To Induce a "Guest-Blocked" Spin Transition in a Framework Material.
2016
A new functionalized 1,2,4-triazole ligand, 4-[(E)-2-(5-methyl-2-thienyl)vinyl]-1,2,4-triazole (thiome), was prepared to assess the broad applicability of strategically producing multistep spin transitions in two-dimensional Hofmann-type materials of the type [FeIIPd(CN)4(R-1,2,4-trz)2]·nH2O (R-1,2,4-trz = a 4-functionalized 1,2,4-triazole ligand). A variety of structural and magnetic investigations on the resultant framework material [FeIIPd(CN)4(thiome)2]·2H2O (A·2H2O) reveal that a high-spin (HS) to low-spin (LS) transition is inhibited in A·2H2O due to a combination of guest and ligand steric bulk effects. The water molecules can be reversibly removed with retention of the porous host f…